There are two basic objectives of our studies: 1) to compare and contrast several mouse models designed to measure the ability of hemopoietic stromal tissue to support hemopoiesis; and 2) to evaluate the type, extent, and duration of damage inflicted on murine marrow and spleen hemopoietic stromal tissue by chemotherapeutic agents. Four murine models to measure the integrity, or hemopoietic support capacity, of hemopoietic stromal tissues (or microenvironment) on control and drug pre-treated mice are being studied: 1) the first model evaluates the ability of the spleens of wholebody lethally irradiated mice to support clonogenic pluripotent stem cell (CFU-S) proliferation by examining spleen nodule formation and spleen nodule size; 2) the second studies hemopoietic compensatory capacity of the spleens of 89Sr marrow-ablated mice; 3) the third determines the amounts of hemopoiesis contained in subcutaneously implanted femurs and spleens (the organs implanted are taken from drug pretreated mice and the hosts are normal mice which have been irradiated); and 4) the fourth measures hemopoietic recuperation in femurs and spleens in drug pre-treated mice after lethal whole-body irradiation and rescue with normal marrow cells. Pluripotent precursor cells (CFU-S) are measured in all studies and granuloid precursor cells (CFU-C), erythroid precursor cells (CFU-E) are measured in selected groups. 99mTc uptake of femurs and spleens are also being evaluated in selected studies. Evaluations are performed up to nine months post cessation of chemotherapy.